I do understand what you're trying to do, but I'm not sure you'll be able to accomplish it, even if you have all of the bikes to test ride. The fact is, you'd have to have the same tires, the same tire pressure, the same saddle, the same
bike fit (stem length, saddle position, bar size, bar position) etc, on each and every bike to compare the ride and know that the difference you feel is in the frame. Besides, those reviews you read describing things like bottom bracket flex, spongy in sprints, turning faster, etc, are written by professional cyclists who just know this stuff incredibly well. Would any of us
really feel those kinds of differences? We're mere mortals, we're not that talented!
Hugs and butterflies,
~T~